Method for controlling an ultrasonic sensor and ultrasonic sensor

ABSTRACT

An ultrasonic sensor has: a diaphragm that includes at least two partial regions for emitting and/or receiving ultrasonic signals, the two partial regions possessing different resonance characteristics; and at least one electromechanical transducer coupled to the diaphragm, to which transducer a control signal having at least two different control signal frequencies is applied. In this context, a first control signal frequency is in the range of a resonant frequency of a first partial region of the diaphragm, and a second control signal frequency is in the range of a resonant frequency of a second partial region of the diaphragm. Alternatively, two electromechanical transducers are used, which are coupled to a diaphragm and have different resonance characteristics.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for controlling an ultrasonicsensor, and to an ultrasonic sensor.

2. Description of the Related Art

Ultrasonic sensors have been used for decades in vehicles forsurrounding-area detection. In this context, the measuring systems arebased on an echo method, in which a transmitted signal is reflected byan obstacle and echoed back to the vehicle in the form of an echosignal. The distance of the obstacle from the vehicle is then determinedwith the aid of the measured echo delay time. This information is thenused for many different driver assistance systems, such as parkingassistance systems or also blind spot monitoring systems. In thiscontext, the ultrasonic sensors are mostly implemented in the form of anultrasonic transducer, which allows switching-over between transmit modeand receive mode.

Conventional ultrasonic sensors include a diaphragm, which, in transmitmode, converts mechanical vibrations in the ultrasonic range intopressure fluctuations of the air surrounding the vehicle, and anelectromechanical transducer, e.g., in the form of a piezoelectricresonator, which is coupled to the diaphragm, e.g., with the aid of anadhesive bond, and, in transmit mode, converts electrical signals intovibrations in the ultrasonic range. In order to give the radiation ofthe diaphragm a direction, it is normally mounted to a chassis, which,in contrast to the diaphragm, is supposed to have negligible vibrationalamplitudes.

As a rule, ultrasonic sensors are operated in the range of theirrespective resonant frequency, which results from the resonancecharacteristics of the respective diaphragm and the respectivetransducer, since particularly efficient conversion of electricaloscillation power into mechanical vibration power, and vice versa, ispresent there.

A method for adjusting the resonant frequency of a vibrating section ofa housing of an ultrasonic sensor, in which the resonant frequency ofthe vibrating section is measured and compared to a previouslyestablished threshold value of a setpoint resonant frequency, is knownfrom published German patent application document DE 10 2006 021 492 A1.In light of the comparison, the resonant frequency of the vibratingsection is adjusted by appropriately removing or applying material.

BRIEF SUMMARY OF THE INVENTION

The present invention provides an ultrasonic sensor, which has adiaphragm including at least two partial regions for emitting and/orreceiving ultrasonic signals, where the two partial regions possessdifferent resonance characteristics, and which has at least oneelectromechanical transducer, which is coupled to the diaphragm, and towhich a control signal having at least two different control signalfrequencies may be applied. In this context, a first control signalfrequency is in the range of a resonant frequency of a first partialregion of the diaphragm, and a second control signal frequency is in therange of a resonant frequency of a second partial region of thediaphragm. In this instance, the different resonance characteristics areadvantageously produced, using different thicknesses of the diaphragm.

In addition, the present invention provides a method for controlling anultrasonic sensor, which has a diaphragm including at least two partialregions having different resonance characteristics, and which has atleast one electromechanical transducer coupled to the diaphragm, where acontrol signal having at least two different control signal frequenciesis applied to the electromechanical transducer. In this context, a firstcontrol signal frequency is in the range of a resonant frequency of afirst partial region of the diaphragm, and a second control signalfrequency is in the range of a resonant frequency of a second partialregion of the diaphragm.

In this context, here and in the following, the wording “resonantfrequency of a partial region” refers to the resonant frequency, whichresults from the resonance characteristics of the diaphragm and theelectromechanical transducer(s) coupled to it.

The present invention is based on the fundamental idea of designing andpositioning the diaphragm and the electromechanical transducer(s) insuch a manner, and controlling the electromechanical transducer(s) insuch a manner, that the ultrasonic sensor has more than one resonantfrequency, at which electrical oscillation power is convertedparticularly effectively into acoustic vibration power, or vice versa.By using ultrasonic signals having different frequencies, it is possibleto improve the ultrasonic-based, surrounding-area detection of a vehiclewith regard to its reliability, range and/or response speed. Thus, forexample, using multifrequency or broadband modulation, echo signals,which are based on transmitted signals that were emitted a relativelylong time ago (long-delay echoes), and/or external or interferencesignals, may be distinguished in a markedly more reliable manner fromechoes, which are the result of signals emitted a short time ago. Inthis context, signals of both the reference vehicle and another vehicleand/or of devices, which are situated in the surrounding area of thevehicle, may be taken into consideration.

According to one specific embodiment of the present invention, thediaphragm may be shaped so that the diaphragm thickness changes in astepped manner. As an alternative to that, a continuous change in thediaphragm thickness may also be provided, which results in a widespectrum of usable signal frequencies.

The diaphragm may be formed to be symmetric or asymmetric as a functionof the specific application case and the specific problem definition,which means that symmetric or asymmetric emitting and/or receivingdirections result accordingly.

The present invention's idea of a multifrequency ultrasonic sensor mayalso be implemented by an ultrasonic sensor, which has a diaphragmincluding at least two partial regions for emitting and/or receivingultrasonic signals, and has at least two electromechanical transducersthat are coupled to the diaphragm and have different resonancecharacteristics, which may be achieved, for example, by differentgeometric dimensions of the transducers. In this context, a controlsignal may be applied to each transducer, the control signals beingindependent of each other and each including at least one control signalfrequency, which is in the range of a resonant frequency of the specificpartial region of the diaphragm.

In order to obtain symmetric or asymmetric emitting and/or receivingdirections, the transducers may be correspondingly coupled to thediaphragm in a symmetric or asymmetric manner.

Corresponding to such an ultrasonic sensor, the present invention alsoprovides a method for controlling an ultrasonic sensor, which has adiaphragm including at least two partial regions for emitting and/orreceiving ultrasonic signals, and has at least two electromechanicaltransducers in each of the partial regions, the electromechanicaltransducers being coupled to the diaphragm and having differentresonance characteristics. According to the present invention, a controlsignal is applied to each transducer, the control signals beingindependent of each other and each including at least one control signalfrequency, which is in the range of a resonant frequency of the specificpartial region of the diaphragm.

An ultrasonic sensor having a diaphragm and at least one electromagnetictransducer, which is coupled to the diaphragm and has at least threeelectrodes, is suited for implementing the fundamental inventive idea,the transducer having different resonance characteristics as a functionof the control of the electrodes. This embodiment has the advantage thata single electromechanical transducer in conjunction with a “classic”diaphragm is already sufficient for implementing a multifrequencyultrasonic sensor.

Accordingly, the present invention also provides a method forcontrolling an ultrasonic sensor having a diaphragm and at least oneelectromechanical transducer coupled to the diaphragm, the transducerhaving at least three electrodes, and a first electrode pair beingcontrolled in order to emit an ultrasonic signal having a firsttransmitted-signal frequency, and a second electrode pair beingcontrolled in order to emit an ultrasonic signal having a secondtransmitted-signal frequency.

A further specific embodiment of the present invention provides that apreferred transmission direction of ultrasonic signals be set with theaid of control signal frequencies of the control signal of thetransducer. To that end, the signal frequencies are set in such amanner, that either the conversion of the electrical oscillation powerinto acoustic vibrational power (transmit mode) is carried out at aresonant frequency, and therefore, particularly effectively, or that theconversion of the acoustic vibrational power into electrical oscillationpower (receive mode) is carried out at a resonant frequency, andtherefore, particularly effectively. Transmitting and receivingfrequencies may deviate from one another, for example, due to Dopplereffects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic sectional view of an ultrasonic sensoraccording to a first specific embodiment of the present invention.

FIG. 2 shows a schematic sectional view of an ultrasonic sensoraccording to a second specific embodiment of the present invention.

FIG. 3 shows a schematic sectional view of an ultrasonic sensoraccording to a third specific embodiment of the present invention.

FIG. 4 shows a schematic sectional view of an ultrasonic sensoraccording to a fourth specific embodiment of the present invention.

FIG. 5 shows a schematic sectional view of an ultrasonic sensoraccording to a fifth specific embodiment of the present invention.

FIG. 6 shows a schematic sectional view of an electromechanicaltransducer of the present invention, having three electrodes.

FIG. 7 shows a top view of a schematic representation of anelectromechanical transducer according to the present invention, havingthree electrodes.

FIG. 8 shows a schematic representation of an ultrasonic sensoraccording to a sixth specific embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the figures, like or functionally equivalent components are eachdenoted by the same reference numeral.

FIG. 1 schematically shows an ultrasonic sensor 1 according to a firstspecific embodiment of the present invention. An electromechanicaltransducer in the form of a piezoelectric resonator 3 is attached to adiaphragm 2 with the aid of an adhesive layer 4 and coupled to diaphragm2 in this manner. A control signal, as a result of which piezoelectricresonator 3 is set into mechanical vibrations, is applied topiezoelectric resonator 3 by a control unit 6 via electrical leads 5.These vibrations are transmitted through adhesive layer 4 to diaphragm2. Diaphragm 2 produces pressure fluctuations in the air in front of it,through which sonic waves are emitted. In order to give the emittedsonic waves a direction, the diaphragm is attached to a chassis 7,which, in contrast to the diaphragm, has negligible vibrationalamplitudes. In the case of receiving sonic waves, the signal pathcorrespondingly runs in reverse, that is, incident acoustic waves areultimately converted into electrical signals.

Diaphragm 2 includes two partial regions 2-1 and 2-2, which havedifferent thicknesses or material strengths that account for differentresonance characteristics of the two partial regions. In the specificembodiment shown, the transition between the two partial regions 2-1 and2-2 is constructed to be stepped, so that in each of the two partialregions 2-1 and 2-2, a resonant frequency results at which electricaloscillation power is converted particularly effectively into acousticvibrational power, or vice versa. By applying a control signal, whichincludes at least these two resonant frequencies or at least twofrequencies in the range of these resonant frequencies, the ultrasonicsensor may be operated simultaneously at two resonant frequencies. Inthis context, a preferred transmission direction of ultrasonic sensor 1,i.e., transmitting or receiving, is set with the aid of the signalfrequencies of the control signal. To that end, the signal frequency iseither selected to be identical to the resonant frequency, so that theconversion of the electrical oscillation power into the mechanicalvibrational power and, therefore, the transmit mode, is optimum; or asignal frequency in the range of the resonant frequency is selected,which results in a possible echo signal having exactly the resonantfrequency and, therefore, an optimum conversion of the mechanicalvibrational power to the electrical oscillation power (receive mode). Inthis context, frequency differences between the transmitted signal andthe echo signal may be due to the Doppler effect, for example.

In the exemplary embodiment shown, piezoelectric resonator 3 is situatedbelow the transition region between partial regions 2-1 and 2-1 ofdiaphragm 2. However, this is not essential to the use of the presentinvention. It is also sufficient for the partial regions of thediaphragm, which have different resonance characteristics, to besituated in a region around an electromechanical transducer.

Such a specific embodiment is illustrated in FIG. 2 This specificembodiment mainly differs from the specific embodiment represented inFIG. 1 in that in a first partial region 2-1′ over piezoelectricresonator 3, diaphragm 2′ has a constant thickness, but that secondpartial regions 2-2′ having increased thickness or material strengthand, consequently, a changed resonance characteristic, are situated onboth sides of piezoelectric resonator 3. In third partial regions 2-3′,via which diaphragm 2′ is attached to chassis 7, the diaphragm again hasthe thickness of first partial region 2-1′ or, alternatively, a further,arbitrary thickness, as well. In order to provide decoupling betweendiaphragm 2 and chassis 7 that is as effective as possible, it isadvantageous to design the edge regions of diaphragm 2′, which aredirectly adjacent to chassis 7, to be as thin as possible. This rule isalso applicable to other exemplary embodiments, which means that inthese specific embodiments, “thinned” edge regions of diaphragm 2 mayalso be provided. However, it should be pointed out that edge regionsconstructed in such a manner are not used for emitting or receiving anultrasonic signal, but solely for decoupling from chassis 7.

The specific embodiment according to FIG. 2 further differs from the oneof FIG. 2 in that the stepped transitions between the individual partialregions are positioned symmetrically, and therefore, diaphragm 2′ isformed symmetrically. Symmetric or asymmetric positioning may allowsymmetric or asymmetric emitting or receiving directions to be achievedin a corresponding manner.

FIGS. 3 and 4 show further specific embodiments of ultrasonic sensorsaccording to the present invention. These differ from the specificembodiment represented in FIG. 1 in that the thicknesses of diaphragms2″ (see FIG. 3) and 2′″ (see FIG. 4) do not change in a stepped manner,but continuously. In particular, the diaphragm 2″ according to FIG. 3 isconvex, and the diaphragm 2′″ according to FIG. 4 is concave. In thismanner, a multitude of partial regions of diaphragm 2″, 2′″ havingdifferent mechanical properties is formed, as it were, which results ina wide spectrum of usable resonant frequencies.

An alternative specific embodiment of an ultrasonic sensor 1″″ accordingto the present invention is represented in FIG. 5. In this context, on a“conventional” diaphragm 2″″ having a constant thickness, twoelectromechanical transducers in the form of piezoelectric resonators3-1″″ and 3-2″″ are attached to partial regions of diaphragm 2″″ withthe aid of adhesive layers 4-1″″ and 4-2″″, respectively, and, in thismanner, are coupled to diaphragm 2″″. In this instance, the twopiezoelectric resonators 3-1″″ and 3-2″″ have different geometricdimensions and also different resonance characteristics caused by them.By applying a control signal in each instance, in which case the controlsignals of the two piezoelectric resonators 3-1″″ and 3-2″″ areindependent of one another and each include at least one control signalfrequency, which is in the range of a resonant frequency of therespective partial region of the diaphragm, this set-up also produces anultrasonic sensor, which is operable at two resonant frequencies. In thespecific embodiment shown, the two control signals are generated by twoseparate control units 6-1″″ and 6-2″″ and applied to piezoelectricresonators 3-1″″ and 3-2″″, respectively, via electrical leads 5-1″″ and5-2″″, respectively. As an alternative to that, the control signals mayalso be generated by a common control unit. Due to the asymmetricset-up, asymmetric emitting and/or receiving characteristics areobtained in a simple manner. Of course, more than two piezoelectricresonators may also be provided, which may also be positionedsymmetrically, if necessary.

A further specific embodiment of the present invention (see FIGS. 6 and7) provides for the use of a piezoelectric resonator 3′″″, which hasthree electrodes 30-1, 30-2 and 30-3. In this context, a first electrode30-1 is situated in the central upper region of piezoelectric resonator3′″″, a second electrode 30-2 is situated in the edge region of theupper side of piezoelectric resonator 3′″″ and a third electrode 30-3 issituated on the lower side of piezoelectric resonator 3′″″. All threeelectrodes 30-1, 30-2, and 30-3 may be controlled by a control unit 6via corresponding electrical leads 5′″″. Due to the positioning and theshape of electrodes 30-1, 30-2 and 30-3, in the case of controlling afirst electrode pair made up of electrodes 30-1 and 30-3, resonancecharacteristics and also directivity characteristics are produced, whichare different from the case in which a second electrode pair made up ofelectrodes 30-2, 30-3 is controlled. If such a piezoelectric resonator3′″″ is coupled to a diaphragm, it is even possible to operate theultrasonic sensor at different resonant frequencies in the case of a“conventional” diaphragm having a constant thickness.

FIG. 8 shows a further specific embodiment of the present invention, inwhich a diaphragm 2″″″ is provided that includes four partial regions2-1″″″, 2-2″″″, 2-3″″″ and 2-4″″″. These are formed in such a manner,that a second partial region 2-2″″″ having a second thickness isrectilinearly contiguous to a first partial region 2-1″″″, which isattached to a left-hand portion of chassis 7. A third partial region2-3″″″ having a third thickness connects to second partial region 2-2″″″at a predefined angle; a fourth partial region 2-4″″″, which has afourth thickness and is attached to the right-hand portion of chassis 7,finally connecting to the third partial region at a further, predefinedangle. In the area of third partial region 2-3″″″, piezoelectricresonator 3 is attached to diaphragm 2″″ with the aid of adhesive layer4 and, therefore, coupled to it. In this specific embodiment, thedifferent thicknesses of the individual partial regions of diaphragm2″″″ also produce different resonance characteristics, which, bysuitable controlling, may be used for implementing a multifrequencyultrasonic sensor. In addition, various preferred orientations of thetransmitted or received signals may be obtained, using thethree-dimensional shape of diaphragm 2″″″.

In addition to the specific embodiments illustrated and described,numerous other specific embodiments of the present invention areconceivable, which result, in particular, from combinations of thespecific embodiments mentioned.

What is claimed is:
 1. An ultrasonic sensor, comprising: a diaphragmwhich has at least two partial regions for at least one of emitting andreceiving ultrasonic signals, the two partial regions having differentresonance characteristics; a chassis attached to the diaphragm, thechassis having negligible vibrational amplitudes; and at least oneelectromechanical transducer coupled to the diaphragm, wherein a controlsignal having at least two different control signal frequencies isapplied to the electromechanical transducer, a first control signalfrequency being in the range of a resonant frequency of a first partialregion of the diaphragm, and a second control signal frequency being inthe range of a resonant frequency of a second partial region of thediaphragm; wherein the electromechanical transducer is attached to thediaphragm by an adhesive layer, and is attached to a control unit viaelectrical leads.
 2. The ultrasonic sensor as recited in claim 1,wherein the different resonance characteristics are produced bydifferent thicknesses of the at least two partial regions of thediaphragm.
 3. The ultrasonic sensor as recited in claim 2, wherein thethickness of the diaphragm changes in a stepped manner between the atleast two partial regions.
 4. The ultrasonic sensor as recited in claim2, wherein the thickness of the diaphragm changes continuously at leastin a transition area between the first partial region and the secondpartial region.
 5. The ultrasonic sensor as recited in claim 4, whereinthe diaphragm is configured symmetrically.
 6. The ultrasonic sensor asrecited in claim 2, wherein the diaphragm is configured asymmetrically.7. The ultrasonic sensor as recited in claim 1, wherein the chassis isdecouplably attached to the diaphragm.
 8. The ultrasonic sensor asrecited in claim 1, wherein an edge region of the diaphragm directlyadjacent to the chassis is thinner than the two partial regions of thediaphragm.
 9. A method for controlling an ultrasonic sensor having adiaphragm which includes at least two partial regions possessingdifferent resonance characteristics, and at least one electromechanicaltransducer being coupled to the diaphragm, the method comprising:applying a control signal having at least two different control signalfrequencies to the electromechanical transducer, a first control signalfrequency being in the range of a resonant frequency of a first partialregion of the diaphragm, and a second control signal frequency being inthe range of a resonant frequency of a second partial region of thediaphragm; wherein a chassis is attached to the diaphragm, the chassishaving negligible vibrational amplitudes; and wherein theelectromechanical transducer is attached to the diaphragm by an adhesivelayer, and is attached to a control unit via electrical leads.